The present invention generally relates to the manufacture of plastic containers and objects, and more particularly, to a method of fabricating plastic objects having a lenticular lens sheet or insert. The fabrication method includes a process of bonding lenticular lens material to the constituent plastic of the container of object during molding processes without damaging the lenticular lens material.
It is a growing practice to utilize conventional plastic molded cups and containers to display promotional messages and to increase the market value of the cups and containers by adding images of sports figures, movie and television personalities and other graphics. While the printing processes for producing these messages, images and graphics have improved in recent years with advances in printing technologies, the messages, characters, and other graphics have generally remained two dimensional, static and non-moveable. The expectations of purchasers of these containers continues to rise, and the general public continues to demand ever increasing and enhanced visual effects in all media. Specifically, the entertainment industry routinely licenses its proprietary images for use on cups, packaging, and containers of all types from plastic soda cups to popcorn containers and their lids. The entertainment industry uses bright colors and molded shapes extensively to excite and interest customers and collectors of these containers. There continues to be pressure from movie makers, sports promoters and others in the entertainment industry to develop new products to better capture the public""s attention for their promotions and licensed products.
In addition to problems with creating more exciting imagery, there are design restraints faced by plastic cup and container manufacturers that must be addressed in creating any new product. For example, in the traditional plastic cup industry, the manufacturers are continuously struggling with the demands for a less expensive cup to make their use attractive as part of no-cost promotional campaigns (e.g., the cup is given away by a retailer with the purchase of soda, beer, or other beverage) and as a profitable standalone product. One method used to reduce cost is to reduce the amount or weight of plastic used in each cup by thinning the cup wall and other methods. Reducing the weight of plastic used reduces material costs and also makes the manufacturing (i.e., molding) of the cups faster and less expensive as the molds can be filled more rapidly and the plastic cools in a shorter time. However, the desire for less material weight and wall thickness must be balanced with the hoop strength of a cup to control the cup being squeezed shut or deformed. Hoop strength is typically measured by adding weights or pressure to a point near the top of the cup on the outer surface of the side wall and measuring the amount of deflection of the open end of the cup.
To further minimize the costs of containers, the inner and outer surfaces of the walls are typically kept smooth and their shape kept relatively simple to minimize mold costs. These smooth surfaces also have been required because the typical method of placing images and graphics on containers and other plastic objects is with standard printing processes, such as offset printing, that are most effective on smooth printing surfaces.
The inventors recognize the needs of the entertainment industry and understand the benefits of providing more visually appealing images and graphics as part of promotional containers and other plastic products. These plastic products are significantly improved by including a three dimensional (xe2x80x9c3Dxe2x80x9d), action image provided with the use of Lenticular lens materials or sheets (i.e., interlaced segments of images combined with Lenticular lenses to provide a variety of visual effects such as motion, zooming in and out, and 3D effects).
The use of Lenticular lens material is known in the printing industry for creating promotional material and typically involves producing a sheet of Lenticular lens material and adhesively attaching the Lenticular lens material to a separately produced object for display. The production of Lenticular lenses is well-known and described in detail in a number of U.S. patents, including U.S. Pat. No. 5,967,032 to Bravenec et al. In general, the production process includes selecting segments from visual images to create a desired visual effect and interlacing the segments (i.e., planning the layout of the numerous images). Lenticular lenses are then mapped to the interlaced or planned segments, and the Lenticular lenses are fabricated according to this mapping. The Lenticular lenses generally include a transparent web which has a flat side or layer and a side with optical ridges and grooves formed by Lenticules (i.e., convex lenses) arranged side-by-side with the Lenticules or optical ridges extending parallel to each other the length of the transparent web. To provide the unique visual effects, ink (e.g., four color ink) is applied to or printed directly on the flat side of the transparent web to form a thin ink layer, which is then viewable through the transparent web of optical ridges.
While these Lenticular lens materials provide excellent visual effects, the use of adhesives and other attachment methods has not proven effective in producing high quality, long-lasting, and inexpensive plastic products. Because attaching the Lenticular lens material after producing the plastic cup or container is inefficient and relatively expensive, the plastic manufacturing industry desires a method for attaching the Lenticular lens material to plastic cups or containers as part of the cup or container manufacturing process. Unfortunately, the plastic manufacturing industry has not been able to overcome the problems associated with using common Lenticular lens material as part of standard plastic fabrication processes. The problems arise because plastic fabrication generally includes processes such as injection molding that involve heating raw plastic materials to a relatively high temperature (e.g., 400 to 500xc2x0 F. or hotter) and then injecting the fluid plastic into a mold with the shape of the desired plastic object or by otherwise processing the molten plastic. The ink or ink layer has a chemistry that does not stay intact when the ink is heated to these high temperatures, and the image is destroyed or at least significantly altered.
To address this problem, the plastic manufacturing industry has made some attempts at protecting the ink layer from the high temperature molten plastics during injection molding processes. Typically, these attempts have involved applying a bonding and protective substrate of hot melt polyethylene to the ink or ink layer to provide protection from the molten plastics and to provide a bonding interface between the Lenticular lens and the plastic of the formed cup or container. The protective substrate material may be as thick as 2.5 mils or more to provide adequate thermal insulation for the ink layer.
While providing a generally effective bonding surface and providing some protection for the ink layer, the application and use of a protective substrate has not resolved all manufacturing problems facing the plastic manufacturing industry. For example, it has proven difficult and often expensive to apply the substrate to the ink layer at a thickness that adequately thermally protects the ink from the high temperature molten plastic during injection molding. Another ongoing challenge has been obtaining adequate opacity behind the lens and ink layer as needed to provide a sharp and colorful image. Typically, proper opacity has been achieved with the use of additional volumes (i.e., thicknesses) of material in the protective substrate which increases costs and adds to manufacturing difficulties of applying thick protective coats on the ink layer.
Another ongoing problem is the thermal protection of the Lenticular lens during the injection molding process. Although the Lenticular lens does not typically come in direct contact with the molten, injected plastic, the Lenticular lens is placed in the female portion of the mold and positioned against an outer wall of the mold. When the male portion of the mold is inserted and the hot plastic, i.e., at or near 500xc2x0 F. is injected into the sealed mold, the female or outer portion of the mold increases in temperatures to approach the hot plastic temperature, such as in the range of 250 to 400xc2x0 F. The serrated surface (i.e., the optical ridges and grooves formed by Lenticules) is a layer formed of APET, PETG, or other material that while having relatively good heat resistance may sometimes deform or flatten during the dwell time necessary to cool and form a cup or container. Of course, any flattening or deforming of these optical ridges can reduce the sharpness of the image or even ruin the focus of the Lenticular lens making the image appear fuzzy and out of focus.
Consequently, there is a need for an improved method of fabricating plastic containers and other objects that include Lenticular lens material mated to plastic. The method preferably addresses the need for a cost-effective method of applying a protective thermal substrate that also provides adequate opacity. Additionally, the fabricating method should be selected to provide improved protection for the Lenticular lens, and particularly, the optical ridges or serrated surface of the Lenticular lens, during injection molding processes to better maintain the focused effect of the lens and ink layer combination on the finished plastic product.
To address the above discussed design constraints and other needs of the plastic manufacturing and entertainment industries, the invention provides an efficient and economical method to produce plastic objects, such as containers, with Lenticular material included as an integral insert (i.e., a Lenticular insert). Significantly, the method provides techniques and features that enhance the achieved image by using an opaque ink for a thermal protective substrate and that reduce the cost of manufacturing the insert by utilizing the coating unit of a lithographic press (rather than a standard ink application unit). Further, the method is designed to provide thermal protection for both sides of the Lenticular insert, i.e., ink used for creating an image and optical ridges formed in an exterior surface of a lens layer. The method produces a plastic object with the features of 3D graphics and/or animated video clips showing a fraction of a second to up to several seconds when viewed through the Lenticular insert from the outer surface of the plastic object.
The Lenticular insert that provides the unique visual imagery includes Lenticular material having optical ridges and grooves on an outer surface and a layer or transparent web of lenses, which together create a relatively rigid material with air passages or voids. A layer of ink is attached to the flat side of the transparent lens layer (and in one embodiment, a bonding primer layer is first applied to the transparent lens layer to enhance bonding). The actual images are pre-printed in this ink layer on the back side or second surface of the pre-extruded or post-embossed plastic lens material, which may be made of a variety of plastic materials including APET, flexible or rigid PVC, styrene, and PETG. The images are interlaced corresponding to the frequency of the Lenticular lens material (i.e., the optical ridges and grooves and the transparent lens layer) and are then printed using offset lithography, web, letterpress, digital, screen, or any other printing process.
According to one aspect of the invention, a method of fabricating plastic products is provided that is effective at integrating Lenticular lens material into the produced plastic product in a cost effective and efficient manner that thermally protects the ink layer of the Lenticular insert. In this method, a Lenticular lens material is provided that is made up of a Lenticular lens layer with an outer surface of optical ridges and an ink layer bonded to a transparent lens layer. A thermal protective substrate comprising ink is applied to the ink layer. In a preferred embodiment, the protective ink is an opaque flexographic ink which enhances the achieved image by providing an opaque background for the ink layer.
Significantly, the use of flexographic ink allows the application of the thermal protective substrate to be achieved using the coating unit of a lithographic press (which enables the efficient application of a thick layer of ink which controls the number of applications required). A Lenticular insert is then formed from the coated Lenticular lens material and the insert is positioned within a mold cavity of a plastic molding assembly. The object is then formed by operating the molding assembly to insert a liquid plastic charge into the mold cavity. The liquid plastic may be in the range of 300 to 700xc2x0 F. and the thermal protective substrate is selected with a thickness ranging from 0.5 to 2 mils to thermally insulate the ink layer from the molten plastic. In one embodiment, a further bonding layer is applied to the thermal protective substrate (such as a UV-curable primer coating or orient polypropylene (OPP)) to increase thermal protection of the ink layer and to enhance bonding between the Lenticular insert and the liquid plastic.
According to another aspect of the invention a method of manufacturing a plastic product with a Lenticular insert is provided that provides thermal protection for both sides of the Lenticular insert during plastic molding operations. The method involves providing a Lenticular insert having a Lenticular lens layer with a first surface of optical ridges and a second surface and an ink layer bonded to the second surface of the Lenticular lens layer. To thermally protect the ink layer, the ink layer is encapsulated with a thermal protective substrate such as an opaque, white UV-curable ink or a hot melt polyester, polypropylene, polyvinyl chloride, or vinyl. The Lenticular insert is positioned within a mold cavity defined by an outer mold body and a center die. The combination of these components defines the dimensions of the plastic product by providing flow paths for liquid plastic. The Lenticular insert is positioned within the mold cavity with the optical ridges adjacent and in heat transfer contact with an insert contacting region of the mold body. Liquid plastic is filled into the mold cavity at a plastic processing temperature (e.g., 300 to 700xc2x0 F.) which causes the center die to be heated to a first operating temperature (e.g., 250 to 400xc2x0 F.).
The method continues with the unique feature of cooling the insert contacting region of the mold body to a second operating temperature which is less than the first operating temperature and also less than about a predetermined deformation temperature of the optical ridges. In one embodiment, the optical ridges are fabricated from APET and the deformation temperature is about 170xc2x0 F. and in another embodiment, the optical ridges are fabricated of PETG with the deformation temperature being about 160xc2x0 F. Thus, the second operating temperature is significantly lower than the first (inner) operating temperature which thermally protects the optical ridges during the dwell steps of forming a plastic object. The first insert contacting region can be thought of as all of the mold body adjacent the optical ridges or a slightly larger or smaller area depending upon the desired results of the Lenticular insert (i.e., whether it is preferable to have a sharply focused image even at edges or to have a very secure bond and plastic frame at edges with possibly blurred edges, respectively).
Other features and advantages of the invention, including a Lenticular insert with an ink thermal protective layer and an inner and/or outer bonding layer, will be seen as the following description of particular embodiments of the invention progresses in conjunction with references to the drawings.